1. Field of the Invention
The present invention relates to a prepreg laminate, constructed from a first prepreg; a second prepreg; and a thermoplastic layer therebetween. In the inventive laminate, at least one of the first prepreg or the second prepreg is made from a matrix resin comprising a benzoxazine-containing composition.
2. Brief Description of Related Technology
Prepregs and prepreg laminates are known. Conventionally, prepregs are prepared from a matrix resin that is based on one or more epoxy resins.
Epoxy resins have been toughened in the past to provide them with more robust performance properties. For instance, mixtures of epoxy resins and phenol-capped polyurethanes are known. Polyurethanes are obtained ordinarily by reacting isocyanates with hydroxy-containing compounds; the resulting polyurethane produces should no longer contain free, phenolic hydroxyl groups. Such polyurethane products may be combined with epoxy resins and amine curing agents to give curable coating agents reportedly distinguished by improved elasticity. See e.g. U.S. Pat. No. 4,423,201 and U.S. Pat. No. 3,442,974.
Epoxy resins can also be mixed with copolymers based on butadiene and acrylonitrile to enhance the impact strength and/or the flexibility of the cured product. However, such copolymers ordinarily compromise the tensile shear strength and the glass transition temperature of the resulting cured products.
U.S. Pat. No. 5,278,257 (Malhaupt) refers to and claims a composition containing a copolymer based on at least one 1,3-diene and at least one polar, ethylenically unsaturated comonomer, a phenol-terminated polyurethane, polyurea or polyurea-urethane of a certain formula, after the removal of the terminal isocyanate, amino or hydroxyl groups, which is soluble or dispersible in epoxy resins, it being necessary for at least one of these groups to be a tertiary amine and where the ratio by weight of the comonomer to the polyurethane, polyurea or polyurea-urethane is from 5:1 to 1:5, and an epoxy resin having at least two 1,2-epoxide groups per molecule.
U.S. Patent Application Publication No. 2005/0070634 describes a composition comprising a) one or more epoxy resins; b) one or more rubber modified epoxy resins; c) one or more toughening compositions comprising the reaction product of one or more isocyanate terminated prepolymers and one or more capping compounds having one or more bisphenolic, phenolic, benzyl alcohol, aminophenyl or, benzylamino moieties where the reaction product is terminated with the capping compound; d) one or more curing agents and one or more catalysts for epoxy resins which initiates cure at a temperature of about 100° C. or greater; and e) optionally, fillers, adhesion promoters, wetting agents and rheological additives useful in epoxy adhesive compositions. The resulting adhesive composition is reported to have a viscosity at 45° C. of about 20 Pa.s to about 400 Pa.s.
Epoxy resins blended with benzoxazines are also known. See e.g. U.S. Pat. No. 4,607,091 (Schreiber), U.S. Pat. No. 5,021,484 (Schreiber), U.S. Pat. No. 5,200,452 (Schreiber), and U.S. Pat. No. 5,445,911 (Schreiber). These reported compositions appear to be potentially useful commercially, as the epoxy resins can reduce the melt viscosity of benzoxazines allowing for the use of higher filler loading while maintaining a processable viscosity. However, epoxy resins oftentimes undesirably increase the temperature at which benzoxazines polymerize.
Compositions of epoxy resins, benzoxazine and phenolic resins are known as well. See U.S. Pat. No. 6,207,786 (Ishida), and S. Rimdusit and H. Ishida, “Development of new class of electronic packaging materials based on ternary system of benzoxazine, epoxy, and phenolic resin”, Polymer, 41, 7941-49 (2000).
Compositions of benzoxazines and curable materials other than epoxy and/or phenolics are also known. To that end, U.S. Pat. No. 6,620,925 (Musa) is directed to and claims a curable composition comprising certain benzoxazine compounds without reactive functionality other than the benzoxazine (apart from allyl and propargyl which are disclosed but not claimed) and a curable compound or resin selected from vinyl ethers, vinyl silanes, compounds or resins containing vinyl or allyl functionality, thiolenes, compounds or resins containing cinnamyl or styrenic functionality, fumarates, maleates, acrylates, maleimides, cyanate esters, and hybrid resins containing contain both vinyl silane and cinnamyl, styrenic, acrylate or maleimide functionality.
In addition, U.S. Pat. No. 6,743,852 (Dershem) discloses combinations of liquid benzoxazines and a thermosetting resin composition for adhering materials with dissimilar coefficients of thermal expansion comprising a) a benzoxazine compound in liquid form, b) thermoset compounds including epoxy, cyanate ester, maleimide, acrylate, methacrylate, vinyl ether, styrenic, vinyl ester, propargyl ether, diallyl amide, aromatic acetylene, benzocyclobutene, thiolenes, maleate, oxazoline, and itaconate, c) optionally, one or more anti-oxidants, bleed control agents, fillers, diluents, coupling agents, adhesion promoters, flexibilizers, dyes and pigments, and d) a cure initiator.
Y. Cui, et al. have reported on the synthesis and characterization of polyurethane/polybenzoxazine-based interpenetrating polymer networks. See Y. Cui, et al., “Synthesis and Characterization of Polyurethane/Polybenzoxazine-Based Interpenetrating Polymer Networks (IPNs)”, School of Chemistry and Chemical Technology, Polymer International, 52:1246-1248 (2003).
T. Takeichi, et al. have reported on the synthesis and characterization of poly(urethane-benzoxazine) films as novel type of polyurethane/phenolic resin composites. See T. Takeichi, et al., “Synthesis and Characterization of Poly(urethane-benzoxazine) Films as Novel Type of Polyurethane/Phenolic Resin Composites”, School of Material Science, Toyohashi University of Technology, 4165-4176 (2000).
To date however it is not believed that prepreg laminates prepared with an interlayer of a thermoplastic material between at least two prepregs have been reported, particularly where at least one of the prepregs is prepared from a matrix resin formulated from benzoxazines.